1. Field of the Invention
The field of the present invention is methods for controlling the supercharge pressure in an internal combustion engine having a mechanical supercharger which is connected to the engine crankshaft and whose internal compression ratio can be varied.
2. Description of the Prior Art
An internal combustion engine having a mechanical supercharger whose internal compression ratio is variable is already known, for example, from Japanese Utility Model Application Laid-Open No. 46435/89 or the like. In the internal combustion engine disclosed in Japanese Utility Model Application Laid-Open No. 46435/89, the supercharger internal compression is controlled in a two-stage manner in accordance with the ratio of the pressure in the discharge side of the mechanical supercharger to the pressure in the intake side. However, the mechanical supercharger is driven by the output power from the engine body, and if the internal compression ratio is switched over without consideration of the engine revolution rate as described above, a large difference between the pressure in the supercharger and the supercharge pressure is produced to cause a discharge pulsing which produces a noise.